Cognitive philosophy - "brain science", as its practitioners call it - is a rarefied academic field. But that hasn't prevented Hollywood from optioning Steve Quartz. Not, alas, for a movie (The Wittgenstein Code?) but for the cutthroat business of marketing them. Quartz, it's thought, can forecast what the notoriously unpredictable audience for film "really" wants better than the audience themselves.

In his laboratory, Quartz uses functional brain imaging, or fMRI, to measure humans' responses to such classics as Casablanca. "Essentially, people are placed inside an enormous magnet," he says. "And then we look to see small changes in blood flow. It's a way of tapping, in a totally non-invasive way, into brain activity."

The moneymen in LA were quick to lease his technique. More money was in prospect - and safer money. As Quartz points out, the margin of profit for the industry is "somewhere in the area of 4%". They need all the help they can get.

It's not just celluloid. Neuromarketing will be the coming across the entire field of retailing. Reading the customer's brain will, Quartz believes, replace the clipboard and stop-you-in-the-street market survey and other primitive research techniques that commerce relies on to get its act right.

The standard view is that you can't foretell what people will want. Has Quartz, with his philosophical know-how and futuristic machinery, solved that problem?

"I think brain science is really beginning to explore the relationship between objective measures and subjective measures of things like taste and preferences," he replies. "When we make a decision there are, of course, conscious components in play. But it turns out that our brain is also tracking a lot of things that we may not be consciously aware of."

So are Quartz and his fellow brain scientists trying to programme us, to turn us into robots? "No, I don't think so. My brain science approach is complementary to the kinds of behavioural things that people have been doing for a long time. It's a way of trying to gauge and measure in areas where, hitherto, we have had very little introspective access. It's a way of getting a new window into those places. And it's more a means of measuring preferences rather than a technique for manipulating choice."

Quartz's ideas cross traditional boundaries. He's both a philosopher and an experimental neurobiologist. And he's also creating a nexus (a very profitable one) between the university lab and the marketplace. Is he happy about that?

"I'm very drawn to that nexus. I think from the philosophical perspective it's a very interesting new development. We are now with brain science where we were 20 years ago with biotechnology - that point in time, for example, when genetics was about to have significant real-world applications. With brain imaging we're at the point where we can look scientifically at decision-making. And from there we too will move on to applications in the political realm, or the economic realm, or the legal realm."

Does he see significant patterns when he puts all the test results together? That women, for instance, prefer different things from men, young people from old people and so on?

"It does work that way. One of the widespread public concerns about brain imaging technology is that it's a way of prying into individuals' minds. The fact is, we're really much more interested in aggregate data with which we can begin to form conclusions about different groups - whether defined by gender, age or demography."

Do his results largely agree with the methods that Hollywood has traditionally used (showing previews to trial audiences), or traditional market survey methods?

"There's some agreement. But we find that with many of the measures we come up with, using brain science, there is no corresponding measure that can be turned up using the traditional methodologies. Those methodologies find some things very difficult, or impossible, to measure. 'Memorability' is a good example of this. If you ask people, 'How memorable is something?' with a view to finding out how long will it stick in their mind, they find it very hard to answer. That information, incidentally, is very important with movies where you may see a trailer months before the film is released.

"We know that there are regions of the brain that are involved in the encoding of long-term memories. And if we look there for activity, we can predict how likely it is that someone will remember in the future having seen this or that item. That's valuable for all sorts of communication strategies in marketing. The modern consumer is inundated with marketing messages - most of which don't make it into our memory at all.

"Another measure that you can't extract with traditional methods is 'salience' - in other words, how interesting a stimulus is for our brain. About 80% of processes in the brain are unconscious and most of those processes are automatically filtering, at their unconscious level, the world around us to decide whether something is worthy of sending upstairs for attention. Only the things that the brain decides are salient, or interesting, get sent up into our conscious mind. You can't interrogate people about things that. So finding out things like that, with brain science, is important. Take something as mundane as picking out a box of cereal, or a magazine cover, from a host of competing similar products. The producer dearly wants to know what will stand out, or capture the consumer's attention.

"The maybe not-so-dirty secret of marketing is that there's not a whole lot of evidence that traditional research works. Typically marketing budgets follow the successful product, rather than the other way around. And even in design, 95% of new products fail. What brain imaging does is to figure a way to find better and more effective ways of offering service to the customer."

So, as they used to say of the customer, the brain is always right?

"Yes, I think that's correct".

· Steven Quartz is director of the Social Cognitive Neuroscience Laboratory at the California Institute of Technology. A list of his publications can be found at steve/quartz